This invention relates to circuit breakers, and, in particular, to a stored energy trip unit for use in a circuit breaker. Accordingly, it is a general object of this invention to provide new and improved devices of such character.
One object of this invention is to provide a new and improved stored energy trip unit, for use in a circuit breaker, which is independent of case stability.
Another object of this invention is to provide a new and improved stored energy circuit breaker trip unit suitable in a variety of housing configurations.
Still another object of this invention is to provide a new and improved stored energy circuit breaker trip unit which is insensitive to inaccuracies in a molded housing, such as post-molding shrinkage, warpage of the housing, and wear of operating parts.
Still yet another object of this invention is to provide a new and improved circuit breaker which is capable of being calibrated prior to assembly in a circuit breaker housing, thereby affording manufacturing economies through the reduction of labor in assembly and disassembly of uncalibrated circuit breakers.
One embodiment of the invention relates to a circuit breaker which includes a movable contact which is adapted to engage with and disengage from a fixed contact within a circuit breaker housing. A contact arm is coupled to the movable contact. Appropriate means causes the contact arm to trip when such means is actuated. The improvement is directed to apparatus for actuating such means including a ferrous material armature latch which is partially rotatable about a housing axis. The armature latch has a first retaining means and a first coupling surface. A striker latch member, partially rotatable about a housing axis, has a second retaining means, a second coupling surface adapted to couple with the first coupling surface, and means for recoupling the second coupling surface subsequent to the second coupling surface becoming uncoupled from the first coupling surface. A spring is coupled between the two retaining means. An electrical circuit, including the contacts, is responsive to an overload current through the circuit breaker for causing the armature latch to partially rotate, uncoupling the two coupling surfaces, whereupon the spring causes the latch member to rotate, providing an impact momentum for actuating the means coupled to the contact arm, thereby tripping the contact arm, and opening the contact. In accordance with certain features of the invention, the armature latch axis and the latch member axis are non-coincident. The two coupling surfaces can have relatively low coefficients of friction.
In accordance with another embodiment of the invention, a circuit breaker includes a movable contact which is adapted to engage with and disengage from a fixed contact within a housing, a contact arm coupled to the movable contact, means when actuated for causing the contact arm to trip, and apparatus for actuating the means. The invention is directed to an improvement wherein the apparatus includes an electrical circuit having a bimetal strip having one end affixed to a load terminal and having an opposite end free to bend when thermally excited. A flexible conductive braid couples such opposite end to the contact arm. The load terminal is fixed with respect to the housing. A ferrous material armature latch is partially rotatable about a point with respect to the housing. The latch has a first end adapted to engage with the opposite end of the bimetal strip, a second end provided with a first retaining means, and an intermediate coupling portion. A latch member, partially rotatable about a point with respect to the housing, has a portion thereof provided with a second retaining means. The latch member has a coupler adapted to couple with respect to the coupling portion, and has an arm for recoupling the coupler subsequent to the coupler becoming uncoupled from the coupling portion. A spring is coupled between the two retaining means. Thus, a small magnitude current overload through the electrical circuit causes the bimetal strip to be thermally excited and bend, moving and partially rotating the first end of the armature latch, thereby uncoupling the coupling portion from the coupler, whereupon the spring causes the latch member to be rotated, providing an impact momentum to actuate the means coupled to the contact arm, thereby tripping the contact arm, opening the contacts. A high magnitude current overload through the electrical circuit sets up a sufficiently strong magnetic field to thereby rapidly attract and partially rotate the first armature latch, thereby uncoupling the coupling portion from the coupler, whereupon the spring causes the latch member to be rotated, providing an impetus to actuate the means coupled to the contact arm, thereby tripping the contact arm, and opening the contacts. In accordance with certain features of the invention, the armature latch point and the latch member point are separate from each other. With certain features of the invention, the coupling portions have relatively low coefficients of friction. With other features of the invention, the ferrous member can be coupled to the bimetal strip.
In accordance with yet another embodiment of the invention, a trip unit for a circuit breaker includes three members. A first member is adapted to pivot about an axis of a carrier member. A second member is adapted to pivot about a separate, spaced-apart axis of the carrier member. A spring connects the first member to the second member so that latching portions thereof, distant from the axes, are latched together forming a triangular geometry. Rotation of the first member about the first axis in an unlatching direction causes the first member to unlatch from the second member. Rotation of the second member about the other axis in a latching direction causes the second member to latch with the first member.
In accordance with still yet another embodiment of this invention, a circuit breaker includes trip unit means, integrally amenable to calibration, and a circuit breaker mechanism located within a housing. The trip unit means is normally not in direct contact with the mechanism. The trip unit means stores energy therein, and, upon actuation of such means, effects tripping of the mechanism.